Diffsonline builds a wide variety of BMW differentials in house to accommodate the several different differential housings used in modern BMW's. We start by cleaning the differential housing, then select the industry's finest ring and pinion gears, apply the desired clutch packs and options, and finally carefully assemble the housing to be shipped to your door.

The first decision to make when buying a custom differential is to determine the gearing you want. The gear ratio determines the number of revolutions of the wheel for every revolution of the drive shaft. The higher the gear ratio, the more RPM's an engine must turn to keep your speed constant. Take a look at our RPM / MPH chart in Technical Information to see how various ratio's may affect your cars performance.

Once you have selected the desired gear ratio, you must determine to what degree do you want limited slip. Limited slip comes with several options from open to 75% and variable ramp lockups. You also can specify the amount and type of clutch's for the differential.

Lastly, there are some upgrade options that may be selected including ring and pinion polishing for reduced friction / lower temperatures, upgraded rear covers, as well as miscellaneous bolts and fluids.